Process of casting



Patented Aug. 1," 1939 UNITED, STATES PROCESS OF CASTING Carl Pie],Solingen, Germany No Drawing.

rial No. 122,211. 1936 2 Claims.

This invention relates to processes of casting and, more particularly,to processes of casting carried out by means of metal or chill-moulds.

The permanent moulds or chills that have i heretofore been used inprocesses of this kind had consistedmf iron, steel or other metals, saidmoulds or chills having frequently been provided, prior to carrying outthe casting process or subsequent to a number of such processes, with acoating at their interior wall, which coating consisted of insulatingmaterials dissolved in water.

A coating of this kind is intended to prevent the formation of achemical compound between the metal of the chill-mould with the metal tobe cast therein. This coating, which had heretofore been applied to themould by hand, for in-' stance by means of a brush, swab or-the like, isconnected with the disadvantage, that the surface of the chill is liableto become of uneven conformation, which will greatly impair theappearance and exactness of the castings. The castings, therefore, canfrequently not be used without an expensive subsequent operation offinishing. A further disadvantage arises in connection with the makingof proper castings from heavy metals, especially from alloys on copperbasis with zinc, tin, lead or similar constituents, by means of metalchills, this disadvantage consisting therein that owing to theimperviousness of the chill the flow of liquid metal within the mouldwill be irregular, with the result that flaws or bubbles are liable tobe present in the completed casting. This naturally renders itdifficult, if not impossible, to make proper castings.

All aforementioned disadvantages, now, are successfully avoided by myinvention by immersing the chill in heated condition into a waterbathprior to each process of casting. This bath according to my inventionfurther contains powdered, insulating materials, such as minerals oroxides, in evenly distributed and floating condition therein. Suchmaterials may advantageously consist of materials that are unable toform gases, for instance of graphite, chalk, clay, oxide of aluminum,argillaceous earth, oxide of zinc, oxide of lead, talc, sand and otherkinds of earth having similar properties.

The chill-mould according to my invention is further heated, to atemperature of about 400 C. or more causing red incandescence of themould and thereupon chilled in said water-bath containing in finedistribution the aforementioned powdered materials. By immersing themould in this highly heated condition into said bath the temperature ofthe latter will be raised Application January 25, 1937, Se-

In Germany January 27,

to boiling, temperature causing the insulating coating which hadremained in the mould from the preceding process of casting in wholly orpartly destroyed condition to be separated from, said mould. After saidmould has been cooled down in said bath, the insulating materialscontained in the latter will deposit on the surfaces of the mould, thusrenewing the insulating coat- I ing that had remained in the mould inpartly or wholly destroyed condition in the form of a perfect anduniform coating. This renewing of the coating due to the drop oftemperature of the mould when being immersed in the bath, is connectedin case of casting alloys of heavy metals containing lead, zinc or tinwith the further advantage that the oxidesformed during casting in themould will deposit on said coating which consists of an amorphousnon-coherent mass.

In this manner said oxides are prevented against depositing on thesurface of the mould itself thus protecting the latter against injury,said oxides being separated from the mould when being immersed in theboiling bath subsequent to each previous process of casting. Aseparation of the deposits of oxides by means of special implements,such as brushes or the like, is not necessary in the present case inorder to obtain smooth surfaces on the castings.

The thickness of the insulating coating so produced on the mould byimmersion depends upon the amount of powdered materials contained in thebath. These powdered materials will produce, subsequent to evaporationof the water of the bath, an insulating coating of even thickness and ofa uniformity that cannot be attained otherwise. By my present processthe mould, as regards the metal to be cast, will be given propertiesnearly as favorable as in case of using a mould consisting of sand, forthe metal while being cast will flow instead of over the rigid andimpervious metal-wail of the mould over said insulating coating formedon the latter by said minerals. As a result of this the metal whilebeing cast will properly and completely fill the mould and move thereinin a quiet and even flow, effectively preventing any formation of flaws,bubbles or the like in the completed casting.

The insulating coating formed by said minerals does not need to presenta fully coherent surface. It may even be of advantage if smallinterstices are present in said insulating coating, as said intersticeswill enclose small amounts of air forming part of the insulatingcoating, the presence of such air having-a favorable effect upon theprocess of casting. In the present case, during casting there isproduced a prwure in the mould, this pressure being due, firstly, to thegravity of the metal present in the mould and secondly to the still moreeffective action of the air cushion which is being formed between theflowing metal and the insulating coating, especially if the latter isnot fully coherent. These small quantities of air now will expand byaction of the high temperature of the metal flowing in the mould and inconsequence of this, in the latter there will be produced a pressureforcing the metal while being cast into the tiniest corners and anglesof the mould, this pressure essentially assisting in the production ofsharp-edged and exactly formed castings that may be used without ,parentand coherent in itself and inseparably time of the mould.

connected with the casting as well as surrounding the latter on allsides thereof. By this, the wall of the mould will be insulated againstthe metal cast thereinto as the formed thin film consists of a masswhich is chemically immune, with the result of ,considerably lengtheningthe life- Besides, by this procedure the castings will be given a smoothsurface of metallic shine giving the last finish to the casting and, inaddition to this, enhancing its resistivity against corrosion, the saidthin film effectively protecting the casting against any outerinfluence.

The aforementioned sudden cooling or chilling of the metal in the mouldwill cause a condensa tion of theadmixtures contained in the meltedmass, said admixtures depositing on the surface of the casting andturning into oxides by action of the high temperature. The high tensionsand pressures produced by sudden cooling or chilling of the metal aswell as the small quantity'of oxygen contained in said thin layer ofoxide will have the effect of transforming said layer into a certainstructure which is quite different from that produced with normal oxidesconsisting of an amorphous mass and forming a layer of considerablethickness. Such oxides are being produced, for instance, by casting indry sand in which case there is slow cooling and unimpeded access ofoxygen from the air during the long period of cooling. Incontradistinction to this, the low temperature of the mould-due toimmersion of the'latter into the bath prior to each process of castingwill produce an extremely thin layer consisting of a precious oxidecovering the surfaceofthecastingintheformofafullyimiform andtransparentfilm.

when commencing the casting, the mould is.

preferably pre-heatcd to the required temperature, while for subsequentcasting the mould is cooled orchilledbyimmersioninth'ebathdowntotherequiredtemperature,inwhichcasethemouldmayremaininthebathifdairedforsom'e longer time eventually forseveral minutes, until it has assumed the proper temperature.

The temperature of the mould prior to each casting process is depmdentupon the composition of the alloy to be cost. If brass or anothercopperalloy containing tin or zinc is used for casting, the temperatureof the mould must be about 100 C. so that a drop of temperatureamounting to about 900 C. will arise between the copper-alloy which iscast at about 1000 C.

into themould and the wall of the latter. In case the copper-alloyincludes constituents which only dimcultly alloy with the copper, suchas for instance lead, a somewhat lower temperature will be required forthe mould in order to effect the heavy chilling of the metal necessaryfor the formation of said film and for producing a uniform covering onthe casting. 0n the bases of experiments I have found that the mostfavorable temperature of the mould amounts in this case to about from 40to C.

In case of copper-alloys containing about from 12 to 15 percent of lead,these .alloys being of especial importance as a substitute fortinbronzes, it is advisable to further chill the casting in still hotcondition after completion of the process by dropping the casting fromthe mould into a water-bath. This further chilling will assist theformation of said film and eflectively prevent the separation of lead.In this manner high-grade castings may also be made from copper-alloyshaving a high content of lead or other constituents that onlydiilicultly alloy with copper. Such copper-alloys could heretoforehardly be cast in chilled moulds, while the castings obtained accordingto my present process may be used without any further finishing that isas a finished product produced solely by cast- The chilling of the metalmoulds which I propose in accordance with my invention by immersing themould into a bath, besides the formation of said film on the surface ofthe casting, is further connected with the advantage that thecastingobtainedbythenewprocesswillbeof afiner structure, especially ifsubsequent to the process the casting is subject to further chilling.

To the copper-alloy there may be added, forinstanceimmediatelybeforetheprocessoicasb ing, a small quantity, aboutone percent, of aluminum which forms a solid solution in copper. Asaresultofthesuddencoolingorchillingduring the casting of the metal inthe mold, which has been chilled below C., the aluminum combines butincompletely, at the top surface, withthe oxygen of the atmosphere. Thusan oxide is formed which is poor in oxygen and posseses entirelydifferent characteristics from ordinary aluminum oxide. The so producedthin layer of non-corrosive aluminum oxide owing to the rapidity ofchilling will be cooled down so effectively that a further diffusion ofoxygen into thecasting', thatisthroughthefilmthereomis renderedimpomble, the same as an exit of the aluminum atom from the oxidemolecule, as the velocityofdiiiusionhasyetbecometoosmallowlngtothecooling whichhastakenplaceinthe meanwhile.

Inprlncipallylikemannerauniformfilmmay be produced all over the surfaceof the castlng, if other film-forming metals such as silicon,manganeseorthelikeareaddedtothecopper-alloy which together with suchadditions is now cast intothe chilledoronly littlepre-heatedmould.

The quantity of additional metal necessary for theformationofhefilmisverysmall and amountsin genual onlyto aboutonepercent of theconstituents of the alloy. It'is of especialadvantageinthiscasethatthesmalladmixtm'e 7 of metals sufficient for theformation of the film does not impair the properties and the characterof the alloy in the casting. The presence of the aforementioned admixedmetals, therefore, can hardly be ascertained.

My present invention, besides for copper-alloys, is also of importanceand advantage for other diflicultly melting metals other than iron, suchas for instance silver; in this case also a protective film may beprovided on the casting rendering it possible to use the same withoutany further finishing.

I claim:

1. A process of making copper alloy castings in metal molds, whichprocess comprises the steps of immersingthe mold into a water bathcontaining powdered insulating material finely dispersed therein untilthe mold has been chilled to a temperature below 80 C. and a thininsulating coating has been formed on its inner surface, and thencasting into said mold an alloy of copper with between 10 and 15 percentlead and about one percent of a substance selected from the groupconsisting of earth metals, silicon and manganese.

2. A process of making copper alloy castings in a metal mold incontinuous succession, which process comprises the steps of immersingthe mold into a water bath containing powdered insulating material untilthe mold has been chilled and a thin insulating coating has been formedon its inner surface, casting into said mold an alloy containing acopper base and a small quantity of a metal selected from the groupconsisting of earth metals, silicon and manganese, whereby the mold isheated to red incandescence and said insulating coating is at leastpartly destroyed by being converted into an amorphous non-coherent masson which some of the metal oxides formed during the casting aredeposited, removing the finished casting from the mold, and reinsertingthe latter while still red hot into said bath, whereby the bath firstcomes to a boil which assists in separating the residua of saidinsulating coating and said oxide deposits from the walls of the moldand then the mold is chilled to the desired temperature while thepowdered insulating materials contained in said bath form a new and,

complete insulating lining, whereupon the mold is ready for anothercasting.

CARL PIEL.

